Devices which enable a golfer to determine distances to targets are known.
One device for measuring distances utilizes sonar techniques to direct a ultrasonic or infrared signal to the pin. The device measures the time elapsed to receive the return signal reflected from the pin. This device requires the golfer to aim the device accurately to the pin, which may be difficult.
Other devices calculate distances by receiving signals from global positioning satellites (GPS). These devices, while accurate, are complex and relatively expensive.
U.S. Pat. No. 3,868,692 entitled "Golf Yardage Finder" is disclosed by Woodward et al. The device comprises a portable unit which selectively receives different RF (Radio Frequency) signals sent by different transmitters located on different pins. The strength of the received signal is proportional to the distance to the pin. Here, the transmitters for each pin are always emitting their signals, which causes more power consumption for the transmitters.
U.S. Pat. No. 4,136,394 entitled "Golf Yardage Indicator System" is disclosed by Jones et al. This device utilizes bi-directional communications between a remote unit and a target unit located on a pin. The remote unit transmits an activation message to the target unit. The target unit responds by emitting a responding message to the portable unit. The remote unit measures the elapsed time between sending the activation message and receiving the responding message to calculate the distance to the pin. Amongst other features, the remote unit also allows the user to provide wind speed information which can be used by the remote unit to indicate how far and where a shot should be aimed to compensate for the wind. However, this invention does not discriminate between response messages sent from different target units which may be near each other. As such, the user will not know what distance is being measured.